3
III.
Structure and Basic Principles
3.1 Basic principles of application
As we all know, the visible light
is a kind of electromagnetic wave with a wavelength of
380nm~780nm. In the statistical law, the corresponding light vibrations happens in possible
directions in the direction perpendicular to
the
light propagation
direction
,
and
the corresponding
amplitude
of light vector
(light intensity
) in
all
possible directions are the same,
usually called
the
natural light.
With certain
devices
(
e.g.,
a polarizer
),
the vibration
direction
can be
fixed in
a
direction
perpendicular to the
light
propagation direction
,
to form a so-called
plane-polarized light
.
When
plane polarized light
goes through
a substance,
the vibration direction
of polarized light
will
turn
an angle
,
the substance
is called
optical
material
, and the
angle
that polarized light
turned is
called
optical rotation
.
If
the plane polarized light
goes through the
optically
pure
substance
,
and
the optical rotation
is determined by
the following three
factors:
(a)
The wavelength (
λ
) of
the plane polarized light:
for different
wavelengths
,
the optical rotation
is different.
(b)
The temperature
(t) of the optically active
substance:
for different temperatures, the optical
rotation
is different.
(c)
The kind
of
an optically active
substance
: for
different
optically active
substances, the optical
rotation
is different
.
The specific rotation [
α
]
t
λ
represents the rotation capacity of a substance.
Typically, the predetermined length of the optical tube is 1dm (100mm), the concentration of the
test substance solution is 1g/mL, and the temperature t
℃
. When the plane polarized light is at the
wavelength
λ
, the measured optical rotation is called the specific rotation of the substance, [
α
]
t
λ
.
The specific rotation is only determined by the structure of substance. Therefore, the specific
rotation is the substance-specific physical constant.
α
t
λ
=[
α
]
t
λ
·L·C (1)
